This invention relates to automotive ignition systems and, more particularly, to a digitally implemented, constant dwell time version thereof.
Electronically controlled ignition systems are well known in the art. Such systems are favored over their mechanical counterpart since the electronic system is more accurate and reliable. Basically, the purpose of any ignition system is to generate a spark suitable for firing the combustion chambers at a predetermined engine angular position. In mechanical breaker point type systems it has been found that spark energy falls off at increasing engine RPM. This may result in inefficient fuel combustion or even engine misfiring. The use of electronic circuitry in the ignition can result in a constant spark energy level over the entire range of engine active operation.
While fully electronic ignition systems have resulted in enhanced engine performance, they have suffered certain limitations. For example, in inductive storage type systems, spark energy level is a function of battery voltage and ignition coil resistance. Each of these parameters is temperature dependent, and, in automotive applications, temperature extremes are to be expected. Prior ignition systems have not compensated for these variables.
A further failing in prior art ignition systems is acceleration response. For proper engine operation, an ignition system must environmental and to accelerations of up to 4,000 RPM per second. Electronic ignitions normally have a time lag, which prevents them from being suitably responsive.
In addition, fully electronic ignitions have required a large number of electronic components, resulting in a very expensive system. Moreover, many of the components are temperature dependent and suffer degradation due to aging effects.